Retarding the increase in viscosity of reclaimed rubber with sodium nitrite



Filed May 1o, 1961 May 18, 1965 R. v. LE BEA-U MEYER RETARDING THE INCREASE IN VISCOSITY OF RECLAIMED RUBBER WITH SODIUM NITRITE United States Patent O 3,184,422 RETARDlNG THE INCREASE IN VSCOSETY F RECLAIMED RUBBER WITH SODIUM NITRITE Ree Vilma le Beau Meyer, Frontenac, Mo., assignor to Midwest Rubber Reclaiming Company, East St. Louis,

Ill., a corporation of Delaware Filed May 10, 1961, Ser. No. 109,188 11 Claims. (Cl. Zoll-2.3)

This invention relates to improvements in the production of rubber reclaim and more particularly to a novel method for retarding the increase in viscosity of rubber reclaims.

Briefly, the present invention is directed to the method 'of retarding the growth of Mooney viscosity values in reclaimed rubber which comprises incorporating certain materials into said rubber.

Reclaimed rubber when stored and in particular when stored at elevated temperatures decreases in plasticity or increases in viscosity. This detracts from the usefulness of the product and may even eventually require reprocessing of the reclaim. This phenomenon is generally known yin the trade and is called growth of Mooney viscosity, the

Mooney viscosity measurement being an accepted measure of the plasticity of rubber reclaim.

Among the several objects of the invention may therefore be noted the provision of a method for effectively and substantially retarding the increase in Mooney viscosity values of rubber reclaims; the provision of such a method which may be conveniently utilized in conjunction with any 'of the conventional reclaiming processes; the provision of a method of this character which may be applied to various types of rubber reclaims consisting in whole or in part of natural rubber, butadiene-styrene type rubbers or mixtures thereof; the provision of a method of this type which permits rubber reclaim products treated thereby to be stored for longer periods of time than was possible heretofore without affecting the usefulness thereof; and the provision of such a method which is simple and economical. Other objects and features will be in part apparent .and in part pointed out hereinafter.

The invention accordingly comprises the methods hereinafter described, the scope of the invention being indicated in the following claims.

The accompanying drawing graphically illustrates the results of tests carried out in accordance with the present invention, which tests will be described in detail herein* after.

As is known, an important characteristic of a finished rubber reclaim product is viscosity or plasticity, as determined by the Mooney viscosity or plasticity test (see Industrial and Engineering Chemistry, vol. 26, page 147, 1934). This method of testing viscosity is well known to those skilled in the art and various types of rubber reclaim products may exhibit Mooney viscosity values ranging, for example, fr-om about 20 to about 80 (at 212 E). The finished rubber reclaim product resulting from a conventional rubber reclaiming process may have a temperature of from about 100 F. to about 160 F. and a relatively low viscosity value. Upon aging and cooling of the product to 74 F. (i.e., room temperature), the Mooney viscosity value increases or grows and eventually attains a fairly constant level. This phenomenon, which makes the rubber reclaim more viscous or less plastic, is particularly noticeable with rubber reclaims consisting in Whole or in part of natural rubber, butadiene-styrene Y type rubbers or mixtures thereof which constitute the more important commercial class of rubber reclaims.

It has been recognized that if the product is in slab form and is cool stacked (i.e., cooled to 74 F. and maintained at this temperature) rather than hot stacked 3,184,422 Patented May 18, 1955 (i.e., stacked at a high temperature, e.g. 140 F., and allowed to cool to room temperature over a period of, say, a week), the growth or increase in Mooney viscosity value takes place more slowly but eventually reaches the same level as that of the hot stacked rubber reclaim. Since the increase in Mooney viscosity value may render the use of the rubber reclaim product objectionable for certain purposes and since this increase in viscosity places limitations upon the length of time for which the rubber reclaim may be stored prior to use, it is desirable to effectively retard or control the growth or increase of the Mooney viscosity.

In accordance with the present invention, it has now been found that the growth of Mooney viscosity values in reclaimed rubber may be retarded by incorporating certain materials, more fully described hereinafter, into the reclaim. The incorporation of such materials into the reclaim results in a substantial retardation of the growth of Mooney viscosity values irrespective of whether the reclaim is hot stacked or cool stacked. The present invention has been found to be effective in retarding the growth of Mooney viscosity Values in various types of natural rubber reclairns consisting in whole or in part of natural rubber, butadiene-styrene type rubbers or mixtures thereof which, as previously mentioned, constitute the most important class of rubber reclaims from the commercial standpoint.

The materials which have been found effective in retarding the growth of Mooney viscosity values include glycol polymers, glycol bottoms, diethylene glycol (either crude or pure), sodium nitrite and mixtures of sodium nitrite and diethylene glycol and sodium nitrite and glycol polymers. The term glycol polymers designates a mixture of monoethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and a condensation of various glycols, and having the following properties: specific gravity (at 60 E), 1.180; distillation range, 390 F. to 580 F.; recovery at 760 mm., atmospheric pressure, approximately This product (commen eially available from G. S. Robins & Co.) is black in color, and contains approximately 40% high molecular weight glycols. The term glycol bottoms designates a mixture consisting of 0.5% by weight of monoethylene glycol, 84.0% by weight of diethylene glycol, 10.5% by weight of triethylene glycol and 5.0% by weight of inerts and having the following properties: boiling range, 220- 290 C., specific gravity, 1.l'-l.l5. The above described materials may be incorporated into the rubber reclaim in varying amounts, but preferably should not exceed 10% by weight based upon the weight of the reclaim or based upon the weight of the rubber scrap where the material is added to the reclaiming mixture.

The method of the present invention may be conveniently carried out in conjunction with any of the conventional rubber reclaiming processes (such as those described in Industrial and Engineering Chemistry, vol. 43, pages '250456, 1951) using conventional reclaiming agents, etc. In general, the retarding agents enumerated above, along with standard compounding ingredients, may be conveniently mixed with the rubber reclaim produced by one of the conventional rubber reclaiming processes and the resulting mixture is then milled and/ or refined in accordance with conventional practice. If desired, the retarding agent can be added directly to the reclaiming mix (i.e., the mixture of rubber scrap, reclaiming agents, etc.) where the heater reclaiming process or mechanical reclaiming process is employed. However, where the digester reclaiming process is employed, the retarding agent must be added to the reclaim after re* claiming and prior to milling and/or refining since the retarding agents, being water-soluble, would otherwise be washed out during the course of the reclaiming procede-1,422

ess. When sodium nitrite is usedv as the retarding agent .Example 1 rubber reclaim produced' by the conventionalV digester process. The reclaim consistedvof a mixture ofsnatural rubber and a.butadiene-styrenentyperubber. Y

In the rst test, two samples'of the reclaim were milled iny accordance with conventional milling vprocedures to produce slabs. VThe Mooney viscosity of each sample was 'The 4Mooney viscosity valueofeach sample was ldetermined, after which the slabs constituting one ofthe sarn- Y ples were" cool stacked, i;e., cooled to 74 E. and maintained atthis temperature, and the slabs constituting the other sample were hot stacked, i.e., placed in an oven at 100V C. and maintained at this temperature.

AfterV a lapse of thirteen weeks, the Mooney viscosity Y,value of each sample Vwas determinedVV and it was found Ythat the Mooney value, of the cool stackedv sample had l0V .v' Y .e `stckd lhd' eaedba' krient f50. A series of tests were carried rout utilizing whole tire a e Sqmp e a mcr s y u mere l 0 increased by yan. increment of 27,5 rand -that of the hot The above described procedure was repeated except j'that 3f parts by Vweight/"of crude diethylene glycol were then determined. The slabs constituting one of the f Y `samples were next cool stacked, .i.e., cooled to "74 Fi and maintained at this temperature, and4 the? Mooney viscosity was again measured'after a lapse ofifour weeks and eight weeksrespectively. The slabs constituting VtheV other sample were hot stackedf Les., placedin Van oven at 140 and cooled down Vto 74'Fl over a period of weeks, respectively.

Inthe second test, the above described procedure was y repeated except` that 3 parts by weight of glycol polymers i jmentof 3.0..V

Vadded to eachV 100 parts by weight -of the reclaim prior to milling@ After thirteen Weeks, Vit Vwas founclthat the Mooney viscosity value of the cool stacked sample had increased-by Yan increment' of 17 and that of the hot stackedfsarnple 0by an increment of 36.

kThe Yabove described procedure was repeated except that 3.,part s by weight of diethylene yglycol and 0.3 part by weight of sodium nitrite werer added to each 100r parts by weight of the reclaim priorto milling. After thirteen weeks, it was found that they Mooney-iviscosity value of the lcool stacked sample had increased by anincreone Week. The Mooney viscosity-of the 4second sample Y' ment 0f`18'-and that of the hot staked. .sample by an was also measured after a lapse of four weeks and eight'` j increment of 33. Y Y

The above described p rocedureGwasV repeatedv except that 3 parts by weight of diethylene glycol and 0.6 part by weight of sodium nitrite were added'to each 100 parts by weight of the reclaim prior to milling. After. thirteen weeks," it was found'that the Mooney viscosity value of .theV-fcoollstackedsamplefhad increased by an-'increment of A12 and that` of1the.hot stacked. sample by an incre- The above described procedure Ywas repeated except that Y 3y parts by weight-of diethylene glycol andv 1 part by also repeated except that 3 partsby Vweightjc'if .glycolV polymers and 1 part by weight of'sodium nitrite'w'ere Y added toeach 100 Yparts byweight of the reclaim prior,l Ato milling and the Mooney viscosity Valueswere not measured after eight'weeks.

The results of these tests are graphically illustrated in` Y the accompanying drawing. Y Y

As shown, in the rst test, the untreated or control reclaim had an initial Mooney viscosity value of approximately 42. Afterifour weeks, the Mooney value of the] cool stacked samplelhad risen toV 52, and after eight Weeks, to'6l. sample, after four weeks, had risen rto V63, and after eight weeks, to 68.

The'Mooney jvalue of the .,hot stacked f weight .of sodium nitrite'were added to each 1700y parts by weightfof reclaim prior to milling. 1 After thirteen weeks,

Vit was' found that therMooneyvis'cosity value of the .cool -stacked'sample had increased by an incrementof 7k and Y that Vof the fhot stacked sample by an increment ofl9.

^The above described pr-ocedure was repeated'except that 'V5 parts by weight of diethylene glycol and 0.5 part by weightfofY sodium nitrite were added to each 100pa1ts by weight of reclaim prior torrnillingr. After thirteen weeks, it was found that the Mooney viscosity value of the cool stacked sample had increased by an incrementl of 10 i and thaty of the hot stacked sample by an increment of 13. x

150 In the .second test, the initial MooneyruviscosityV valueVV of the treated samples' was approximately 37. After'fourweeks, the Mooney value Vof the cool stacked sample had risen kto. approximately 44, and after eight Weeks,'to 49. Y The Mooney value of the hot stacked? sample,.after four weeks, had risen to approximately 491,. and afteri eight Weeks, to about 54.

In Ythe third test, the initial Mooney viscosity value 'Y of the samples wasapproximately 36. After four weeks,

the Mooney value of the cool stacked sample hadrrisen to 4l, and after eight weeks, to 46. The YMooney value A of the hot stacked sample, after four weeks, haiilriserl` to 43, and after eight weeks, to 48. Y s

In the fourth test, the initial Mooney'value yA Whole-tire rubber reclaim produced by the convenof they samplesr was'35. After four weeks, the Mooney value. of Vthe cool stacked sample had risen tol 38, and thel tional heater process was employed.` The reclaim con- Y sisted of a mixture of naturalrubber and a butadienestyrene type rubber. Y

Two samples of the reclaim were milled in accordance with conventional milling procedures toY produce slabs..

The above .described `procedure was repeated except that 5 parts Vby Wei'glitofldiethylene glycol were .added to each 100 partsby `weight of reclaim prior to milling.

. After thirteenpweeks, `it' wasfound that the Mooney vis- Vcosity valueV of the '.cool stacked sample had increased by lan increment of 9 land that of the .hot stacked ysample-by an increment of 22.

yThe Vabove describedfprocedure was again repeated except that 5 partsr by weight of glycol polymers were added toV eachl00.parts by weight of reclaim prior to milling. Aftery thirteen weeks, it was found that the Mooney viscosity value of the cool stacked sample hadV increased by an increment ofY 8 and `that of the ho stacked sample by-anfincrement of 22.v f

Y lExample 3 ik A lfiber-freewliole'tireprubber reclaim produced by the conventional mechanical process was employed. The reclaimk consisted lof a mixtureiof natural rubber and a butadiene-styrene type rubber.

'Two samples of the reclaim were milled and rened -in' accordance .with conventional procedures to produce slabs. The Mooney viscosity value of each sample was determined,afterrwhich the slabsfconstituting one of the samples were cool stacked, i.e`., cooled to 74 F. and maintained 'at this temperature, and the slabs constituting the other sample were hot stacked, i.e., placed in an oven at 100 F. and maintained at this temperature.

After a lapse of thirteen weeks, the Mooney viscosity value of each sample was determined, and it was found that the Mooney viscosity value of the cool stacked sample had increased by an increment of 25 and that of the hot stacked sample had increased by an increment of 52.

The above described procedure was repeated except that parts by Weight of sodium nitrite were added toeach 100 parts by Weight of the reclaim prior to milling and refining. After thirteen Weeks, it was found that the Mooney viscosity value of the cool stacked sample had increased by an increment of 8 and that of the hot stacked sample by an increment of 26.

The above described procedure was repeated except that 5 parts by Weight of diethylene glycol were added to each 100 parts by weight of the reclaim prior to milling and refining. After thirteen weeks, it was found that the Mooney viscosity value of the cool stacked sample had increased by an increment of 14 and that of the hot stacked sample by an increment of 33.

Example 4 A natural rubber reclaim produced by the conventional digester process was employed.

Two samples of the reclaim Were milled in accordance with conventional milling procedures to produce slabs. The Mooney viscosity value of each sample was determined, after which the slabs constituting one of the samples were cool stacked, i.e., cooled to 74 F. and maintained at this temperature, and the slabs constituting the other sample were hot stacked, i.e., placed in an oven at 100 F. and maintained at this temperature.

After a lapse of thirteen weeks, the Mooney viscosity value of each sample was determined, and it was found that the Mooney viscosity value of the cool stacked sample had increased by an increment of 37 and that of the hot stacked sample had increased by an increment of 62.

The above described procedure was repeated except that 10 parts by weight of sodium nitrite were added to each 100 parts by Weight of the reclaim prior to milling. After thirteen Weeks, it was found that the Mooney viscosity value of the cool stacked sample had increased by an increment of 16 and that `of the hot stacked sample by an increment of 47.

The above described procedure was repeated except that live parts by weight of diethylene glycol were added to each 100 parts by Weight of reclaim prior to milling. After thirteen weeks, it was found that the Mooney viscosity value of the cool stacked sample had increased by an increment of l5 and that of the hot stacked sample by an increment of 28.

Example 5 A rubber reclaim made from tread bufiing stock and consisting of a butadiene-styrene type rubber was employed. The material had been reclaimed by the heater process.

Two samples of the reclaim Were milled in accordance with conventional milling procedure to produce slabs. The Mooney viscosity value of each sample was determined, after which the slabs constituting one of the samples were cool stacked, i.e., cooled to 74 F. and maintained at this temperature, and the slabs constituting the other sample were hot stacked, i.e., placed in an oven at 100 F. and maintained at this temperature.

After a lapse of thirteen Weeks, the Mooney viscosity value of each sample was determined, and it was found that the Mooney viscosity value of the cool stacked sample had increased by an increment of 20 and that of the hot stacked sample had increased by an increment of 38.

The above `described procedure was repeated except lthat 10 parts by weight of sodium nitrite were added to each parts by weight of the reclaim prior to milling. After thirteen weeks, it was found that the Mooney viscosity value of the cool stacked sample had increased by an increment of 8 and that 'of the hot stacked sample by an increment of 28.

The above described procedure was repeated except that 5 parts by weight of diethylene glycol were added to each 100 parts by Weight of the reclaim prior to milling. After thirteen weeks, it Was found that the Mooney viscosity value of the cool stacked sample had increased by an increment of 8 and that of the hot stacked sample by an increment of 21.

In each of the above examples, the Mooney viscosity value was determined in accordance with the procedure of ASTM D1646-59Tat 212 F., 3 minutes and using the large rotor.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes should be made in the above methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. The method of retarding the increase in viscosity of reclaimed rubber selected from the group consisting of natural rubber, a butadiene-styrene rubber and mixtures thereof, which comprises incorporating `into said rubber not more than approximately 10% by weight, based upon the weight of the rubber, of a material selected from the group consisting of sodium nitrite; a mixture of diethylene glycol and sodium nitrite; and a mixture of glycol polymers and sodium nitrite.

2. The method of retarding the increase in viscosity of reclaimed rubber selected from the group consisting of natural rubber, a butadiene-styrene rubber and mixtures thereof, which comprises incorporating into said rubber approximately 10 parts by Weight of sodium nitrite per 100 parts by weight of rubber.

3. The method of retarding the increase in viscosity of reclaimed rubber selected from the group consisting of natural rubber, a butadiene-styrene rubber and mixtures thereof, Which comprises incorporating into said rubber approximately 3 parts by Weight of diethylene glycol and not more than approximately 1 part by weight of sodium nitrite per 100 parts by Weight of rubber.

4. The method of retarding the increase in viscosity of reclaimed rubber selected from the group consisting of natural rubber, a butadiene-styrene rubber and mixtures thereof, which comprises incorporating into said rubber approximately l5 parts by Weight of diethylene glycol and not more than approximately 1 part by weight of sodium nitrite per 100 parts by weight of rubber.

5. The method of retarding the increase in viscosity of reclaimed rubber selected from the group consisting of natural rubber, a butadiene-styrene rubber and mixtures thereof, which comprises incorporating into said rubber approximately 3 parts by Weight of glycol polymers and not more than approximately l part by weight of sodium nitrite per 100 parts by weight of rubber.

6. The method of retarding the increase in viscosity of reclaimed rubber selected from the group consisting of natural rubber, a butadiene-styrene rubber and mixtures thereof, which comprises incorporating into said rubber prior to milling thereof a material selected from the group consisting of sodium nitrite; a mixture of diethylene glycol and sodium nitrite; and a mixture of glycol polymers and sodium nitrite.

7. The method of retarding the increase in viscosity of reclaimed rubber selected from the group consisting of natural rubber, a butadiene-styrene rubber and mixtures thereof, which comprises incorporating into said rubber prior to milling thereof not more than approximately of rubber.

10% by Weightbase'd upon the weight of the rubber, of

Va material selected from the group consisting of sodium nitrite; a mixture of diethylene glycol and sodium nitrite; and a mixture of glycol polymers and sodium nitrite;

8. The method of retarding the increase in viscosity of part by weight of sodium nitrite per 100 parts by weight Vof rubber. i

reclaimed rubber selected from the group consisting of natural rubber, a butadiene-styrene rubber and mixtures v Y thereof, which comprises yincorporating into said rubber Vprior to milling thereof approximately 3 parts by Weigh-t of diethylene glycol and not more Vthan approximately l par-t by Weight of sodium nitriteper 100 lparts by Weight 10. The method of retarding the natural-rubber, a butadiene-styrene rubber and mixtures thereof, which comprises incorporating into said rubber increase in viscosityk of reclaimed rubber selected from thegroup consisting 'of priorV to milling thereofaapproximately 5 par-ts by weight of diethylene glycol and not more than approximately 1 11. The method of reta'rding the increase invvisco'sity of reclaimed rubber selected from the group consisting of naturalgrubber, a butadiene-styrene rubber and mixtures thereof, vwhich comprises 'incorporating in-to said rubber prior toV milling'thereof approximately 3 parts by weight of glycolvpolymers and not'rnore than approximately 1 part by weight of sodium nitrite per v100 parts by weight lof rubber. Y Y

References Cited'by the Examiner UNITEDl Y STATES PATENTS k12/50 Johnson et al. 26o-2.3 3,055,193 11/62 Voir 26o- 45.9

MURRAYATILLMAN, Primary Examiner. VVLEON J. BERCQVITZ, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,184,422 May 18, 1965 Ree Vilma 1e Beau Meyer It s hereby certified that error appears in the above numbered patent reql'lring correction and that the said Letters Patent should read as cnzrectedbelow.

Column 2, line 23, strike out "natura1"; Column 4,

line for "100 C read 100 F Signed and sealed this 5th day of October 1965.

(SEAL) Attest:

ERNEST W. SWIDER Amesting Officer EDWARD J. BRENNER Commissioner of Patents 

1. THE METHOD OF RETARDING THE INCREASE IN VISCOSITY OF RECLAIMED RUBBER SELECTED FROM THE GROU CONSISTING OF NATURAL RUBBER, A BUTADIENE-STYRENE RUBBER AND MIXTURES THEREOF, WHICH COMPRISES INCORPORATING INTO SID RUBBER NOT MORE THAN APPROXIMATELY 10% BY WEIGHT, BASED UPON THE WEIGHT OF THE RUBBER, OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF SODIUM NITRITE; AND A MIXTURE OF GLYCOL ENE GLYCOL AND SODIUM NITRITE; AND A MIXTURE OF GLYCOL POLYMERS AND SODIUM NITRITE. 